The present invention relates in general to three prong extension and power lines, and in particular, to a new and useful three prong extension and power line having a redundant ground connection.
Extension cords and power lines for many electrical appliances and devices which are designed to operate on 120 volt single phase power, often include two blade shaped prongs which are respectively connected to hot and neutral poles of the one phase power supply. A ground is often also used for a plug and socket of such lines and extension cords, which is connected to the neutral terminal of the power supply. This neutral terminal is grounded so that the third prong acts as a ground connection for the electrical device or appliance.
The ground prong is electrically connected to the housing or any exposed metal surfaces of the appliance or device. In case an accidental bridge is formed between the hot terminal of the power supply and the housing, electricity flows through the ground prong to the ground connection of the power supply. This avoids having the electricity go through a person holding the housing, resulting in electrocution.
The foregoing system operates correctly as long as the proper terminals of the power supply are connected to the proper terminals of the extension cord or appliance.
It often occurs, however, that improper connections are made to the power supply. The most common error is to reverse the hot and neutral connections. While this may seem to be an innocuous error, in view of the fact that the power supply is alternating current, this error can lead to electrocution if it is compounded by other errors in wiring the extension cord or power line of the appliance.
These types of errors in wiring have often been linked with unexplained electrocutions. Such electrocutions often happen in a hospital environment. A large number of appliances and devices are wired and used in a hospital. This increases the chances for wiring errors and thus the chance of inadvertently electrocuting a patient who is utilizing the devices.
In an attempt to avoid these problems, the present inventor proposed in U.S. Pat. No. 4,025,139, a redundant electrical grounding system which utilized an extra ground prong and an additional wire. This use of a redundant ground would thus minimize the chances of error in wiring both the power supply and the power cord for an appliance.
This invention did not meet with commercial success, however, since the industry was reluctant to abandon the conventional three prong arrangement for wall plugs.
In the meantime, however, reports of unexplained electrocutions have continued.
In the April 1982 issue of Science Digest, an article entitled "Cures That Kill" disclose how some deaths rather than being caused by a disease for which the patient was being treated, was actually caused by inadvertent electrocution.
A June 18, 1985 article in the STAR reported an investigation conducted by Ralph Nader into the medical profession concerning the accidental electrocution of 5000 patients a year of electrical equipment.
Reports of unexplained electrocutions continue to the present day.
Many, if not all, of these can be traced to improper wiring. If, in fact, a correctly grounded electrical device were utilized, these types of electrocutions would not be possible.
Conventional three prong plugs, having a narrow blade for the hot connection, usually carrying a black wire, a broad blade for the neutral connection, usually carrying a white wire, and a grounding prong for a ground connection, usually carrying a green wire, can be conencted to a three wire line in six possible ways, only one of which being the correct connection. In other words, the black and white wires may be reversed. The white and black wires may be reversed, etc. This plug, whether it is correctly wired or not, can be inserted into an outlet which itself may be correctly wired or not.
By the same token, a female connector body of an extension cord can be wired in one correct way and five incorrect ways.
The various combinations which are possible yield one perfectly correct wiring combination (labeled OK in the following tables), several improperly wired yet generally safe combinations (where a dash appears in the table) or the immediate hazard of electrocution (labeled X in the following tables).
In each of the tables, the left-hand column starts at the top with the piece of hardware to be wired (whether it is the male plug of the device or an extension cord, or the female socket of the extension cord), each with a black (B), white (W) and ground (G) screw or connecting site. Below the listing of these connecting sites are the color designations of three wires which can be connected to these sites. While normally these wires are black, white and green, respectively, many line cords and wires have uncolored and undistinguishable wires. Add to this the fact that many dozens of pieces of equipment and extension cords may be assembled at one sitting, and the possibility of making any one of the errors in wiring exists.
It is interesting to note in Tables 2 and 3, that even properly wired extension cords can act as an conduit to cause an electrocution. An investigation would not reveal the true cause of heart failure and an electrocution could go undetected.
TABLE 1 ______________________________________ Male 3 Wire Plug and Line Cord to be Connected to a Device Plug Con. Sites Properly Wired Reverse Polarity B W G Outlet Outlet ______________________________________ B W G OK -- B G W -- X W B G -- -- W G B -- X G B W X -- G W B X -- ______________________________________ B = Black Site or Wire W = White Site or Wire G = Ground Site or Wire OK = Correct Wiring, No Hazard -- = Incorrect Wiring, No hazard X = Incorrect Wiring, Electrocution Hazard
TABLE 2 ______________________________________ Male 3 Wire Plug and Line Cord to be Part of an Extension Cord Plug Con. Proper Outlet Rev. Outlet Site Proper Rev. Pola. Device with Device with B W G Outlet Outlet Rev. G & W Rev. G & W ______________________________________ B W G OK -- -- X B G W -- X -- -- W B G -- -- X -- G B W X -- -- X W G B -- X X -- G W B X -- -- X ______________________________________
TABLE 3 ______________________________________ Female 3 Wire (Socket) Connector and Line Cord to be Part of an Extension Cord Socket Con. Proper Outlet Rev. Outlet Site Proper Rev. Pola. Device with Device with B W G Outlet Outlet Rev. G & W Rev. G & W ______________________________________ B W G OK -- -- X B G W -- X -- -- W B G -- -- X -- W G B X -- -- -- G B W -- X X -- G W B X -- -- X ______________________________________
These tables are presented to show the possible errors that can be made in wiring, and the sometimes dire results which may come about. These dangers of electrocution are compounded by mechanical failures that could also occur in the devices, such as the case where the hot or black wire is frayed or damaged and makes inadvertent contact with the metal casing or chassis of the device.
It is noted that the tables show the possibility of electrocutions where perfectly good outlets and devices are utilized, but where the errors are in how they are wired.
The X designation for an electrocution hazard means that 120 volts are available directly at the device chassis or housing. In the case of a drill having a metal handle for example, this would mean that any person holding the drill would be directly connected to 120 volts. The actual passage of current through the person would rely on how well insulated the person is from the ground. If, for example, a person is standing in water, immediate electrocution would most likely occur.